Chemistry - Unit 11: Kinetics and Equilibrium

kinetics

study of how fast a chemical reaction is occurring and describes the rate of change in the concentrations of the reactants and products over time in chemical rxn

collision theory

reaction is most likely to occur if the reactant particles collide with sufficient energy and proper orientation

Factor that affect rate of reaction:

Temperature

temp increases, rate of chemical rxn increases

higher temps=particles collisions more frequently and with more energy

Factor that affect rate of reaction:

Surface Area

surface area increase=rate of rxn increase

Factor that affect rate of reaction:

Concentration

concentration increase= rate of rxn increase

Factor that affect rate of reaction:

Pressure (gas only)

pressure increase=rate of rxn increase and more effective collisions

Factor that affect rate of reaction:

Presence of a catalyst

catalyst presence=rate of rxn increase

gives an alternate reaction pathway which requires less energy than the normal

Factor that affect rate of reaction:

Nature of Reactants

Ions in water = fast

gases are FASTER than solids and liquids

ions FASTER than molecules

Catalyst & alternate reaction pathway

lower activation energy

endothermic chemical reaction

exothermic chemical reaction

Heat of Reaction

- change in enthalpy

△H = PE products - PE reactants

-△H=exothermic

+△H=endothermic

Reaction Mechanisms

series of rxn steps that have to occur for a rxn to go to completion that are determined by experimentation

intermediates

species produced in one step that become reactants in a subsequent step

Reaction Rate Laws

rate = k [A][B]

k (specific rate constant)

depends on the size, speed, and kind of molecule at a given temperature

rate law experssion

rate of chemical rxn is proportional to the product of the [ ] of reactants raised to the power of the coefficents

rate of multi-step rxns

product of the [ ] of the reactants in the slowest step

equilibrium

- rates of forward = rate of reverse

- concentrations of reactants and products stay CONSTANT

Solution Equilibrium

when a solution is saturated

Phase equilibrium

rate of condensation/melting = rate of evaporation/freezing

chemical equilibrium

concetration of reactants and products remain constant

rates of forward and reverse are equal

equilibrium expression

Keq

shows the extent to which the reactants are converted to products

AT EQUILIBRIUM

RATES of opposing rxns are EQUAL

solubility product constant

Ksp

values are always SMALL

Le Chatelier's Principle

if stress to a system at equilibrium, the equilibrium will shift to reduce of alleviate the stress

Stressors of system @ equilibrium

- concentration

- temperature

- pressure (only gases)

Describe the shift given that reactants are on the left and products are on the right:

add reactant

right

the other reactants DECREASE as products INCREASE

trying to balance the products by making more so shifts right

Describe the shift given that reactants are on the left and products are on the right:

add product

left

the other reactants INCREASE as products DECREASE

trying to balance the reactants side by making more so shifts left

Describe the shift given that reactants are on the left and products are on the right:

remove reactant

left

the product DECREASES as the reactants INCREASE

trying to balance the reactants side since there isnt enough reactant to make the product

Describe the shift given that reactants are on the left and products are on the right:

remove product

right

the product INCREASES as the reactants DECREASE

trying to balance products side to make more products

TRICK FOR LE CHATELIER with concentration stressors and temperature

DISCLAIMER: IF YOU DO NOT UNDERSTAND THIS RIGHT AWAY, PLEASE SKIP. I DON'T WANT TO CONFUSE ANYONE AND THEN GET BLAMED FOR IT lol

Whichever side has less stuff, that the side the equilibrium will shift.

for example,

N2 + 3H2 <-> 2NH3 + 22.0 kcal

if H2 is removed, theres less "stuff" on the reactant side so the shift would be left

if N2 is added, there is less "stuff" on the product side, so the shift is right

if temp increases, theres less stuff on the reactants side, so the shift would be left

Describe the shift given that reactants are on the left and products & temperature are on the right:

increase temperature

left

the reactants INCREASE and the products DECREASE

the endothermic process is favored

the more energy/temp there is, the more of the reactants side can be made

Describe the shift given that reactants are on the left and products & temperature are on the right:

decrease temperature

right

the reactants DECREASE and the products INCREASE

the exothermic process is favored

the less energy/temp there is, the less of the reactants side can be made so it tilts towards the products side

Describe the shift given that reactants are on the left and products & temperature are on the right:

increase pressure

right

only works for gases and favors LESS mols of gas

the reactants DECREASE and the products INCREASE

Describe the shift given that reactants are on the left and products & temperature are on the right:

decrease pressure

left

the reactants INCREASE and the products DECREASE

only works for gases and favors MORE moles of gas

entropy

measure of randomness represented by +/-△S

entropy increases or decreases:

solid -> liquid -> gas

increase

affect of synthesis

decrease in entropy

affect of decomposition

increase in entropy

affect of gas

the more moles of gas, the greater the entropy

Gibb's Free Energy

spontaneous reactions

HIGH entropy & LOW energy & exothermic

-△G = -△H - T * +△S

non-spontaneous reactions

+△G = +△H - T* -△S

spontaneous under low temp

-△G = -△H - T * -△S

spontaneous under high temp

-△G = +△H - T * +△S

to be spontaneous, the △G must be ...

negative